INTERCRYSTALLINE FRACTURE IN AN INTERNALLY OXIDIZED BCC ALLOY.

Intercrystalline fracture resulting from tensile deformation at low temperature, defined here as a temperature low enough that diffusion effects can be ignored, has been observed in several age-hardenable alloys having either a bcc or fcc matrix structure. These investigations have generally shown the alloys to have short elongation to fracture when aged to near maximum strength. The grain boundary facets on the fracture surface may be brightly reflective, and may be covered with a fine microdimple dispersion. These fractures are often termed brittle, although the existence of microdimples implies that localized shear fracture may have occurred. The relationship between fracture path, the precipitate free zone (PFZ), and the role of grain boundary precipitate is not clear, particularly in the case of the bcc alloys studied, because the grain boundary precipitate was thought to be the alpha -hcp form of either Hf or Ti, which is ductile at room temperature. The present work extends the fracture morphology study to a ductile bcc alloy precipitation hardened by oxide particles.